U.S. Pat. No. 5,667,827 of Dennis J. Breen discloses a packaging system for preserving meat in which an oxygen-impermeable tray is disposed within a gas impermeable outer barrier bag, the barrier bag is evacuated, and the barrier bag is then flushed with carbon dioxide. In Column 3 of this Breen patent, the patentee states that "The tray 12 is preferably made from a material which is impermeable to or does not retain residual oxygen." In the claims of the Breen patent, reference is made to " . . . a tray formed of a gas barrier material . . . ."
The Breen patent teaches away from the use of gas permeable foamed trays in his packaging system. Thus, in column 1 of his patent, Breen teaches that "In the case where styrofoam packing trays are used, however, residual oxygen is trapped inside the porous openings of the styrofoam tray material and eventually diffuses out over time, thereby causing premature discloration and bacterial decay of the meat."
U.S. Pat. No. 5,950,402 of Richard Hoddinott also discloses the disadvantages of gas permeable foam trays in such packaging systems, stating that "Our work has shown that the discolouration experienced by meat packers using plastic bags and carbon dioxide arises from the use of foamed polystyrene trays because the occluced air in the trays equilibrates with the carbon dioxide in the pouch and becomes available to the surface of the meat." However, the Hoddinott patent also discloses that "In the instances where nonfoamed plastic trays less than 1 mm thick are used, no gas release is expected but these are more expensive and less familiar to the consumer than thicker foam trays. Accordingly, meat packers wish to retain the use of trays which are already familiar to those in the industry."
In order to use foam trays in his packaging system, Hoddinott teaches a process in which the air in the interstices of the foam tray is exchanged for a packaging gas (such as carbon dioxide) prior to the time the containers are used for packaging of food, and thereafter the tray so treated is disposed within a gas tight storage receptacle which is then flushed with the packaging gas and then sealed.
The Hoddinott process is relatively complicated and expensive. Furthermore, it is not always effective. Once the foamed tray has been treated to remove oxygen from its interstices, it must have the item to be preserved disposed on the tray; and therafter the assembly must be disposed within the barrier bag. If any of these steps are done in an atmosphere which contains oxygen, there is a substantial risk of gas exchange between such oxygen and the packaging gas within the interstices of the foamed tray. Thus, in order to be effective, all of the steps of the Hoddinott process should be conducted within an inert atmosphere. Living beings cannot survive within an inert atmosphere; thus, the Hoddinott process must be accomplished by machine means.
It is an object of this invention to provide a packaging system which is as effective if not more effective than the system of Hoddinott but does not require the controlled atmosphere conditions called for by the Hoddinott process.